1. Field of the Invention
The present invention relates to a semiconductor memory device, and more particularly to the wiring of sense amplifiers and the like of a semiconductor memory device.
2. Description of the Prior Art
A semiconductor memory device has in general a memory cell array region formed by arranging memory cells with digit lines and word lines connected thereto in an array form. In the direction parallel to the digit lines of the memory cell array region there are provided X decoders that are connected to the word lines, and in the direction parallel to the word lines there are provided Y selectors and sense amplifiers that are connected to the digit lines.
In such a semiconductor memory device, a word line is formed of polycrystalline silicon with a relatively high resistance value (about 20 .OMEGA./square). Consequently, the length of the word lines has to be made as short as possible in designing a memory with high speed. A method of diminishing the length of the word lines is to reduce the number of digit lines in order to decrease the length in the direction of the word lines within the memory cell array region. In accordance with this method, the number of the memory cells that are connected per digit line is increased by augmenting the length of the digit lines in proportion to the degree of reduction in the number of the digit lines.
Among memories for which high speed is required, in a memory with a large number of output bits such as a micro ROM that is storing micro codes and a cache memory the number of the sense amplifiers becomes large corresponding to the number of the output bits. Since the sense amplifier circuits are formed in the direction of the word lines of the memory cell array region, as mentioned above, which becomes narrow by the aforementioned arrangement, the available width of the formation per sense amplifier circuit becomes small.
In short, in a memory device which requires high speed and has a large number of output bits, the width of the region for forming the sense amplifiers is narrow so that there is a drawback in that it is not possible to obtain a complicated circuit with large number of elements, namely, a sophisticated sense amplifier circuit.